Production of titanyl sulfate solutions

ABSTRACT

A titanium- and iron-containing slag is ground, the iron is magnetically separated and the balance is decomposed with sulfuric acid to produce a titanyl sulfate solution which is further treated to render it suitable for preparation of superior titanium dioxide pigments. Specifically, a portion of the ultimate titanyl sulfate solution is subjected to reduction by the addition thereto of magnetically separated iron and sulfuric acid, the reduction being carried out to give a titanium(III)content of about 50 to 90 grams per liter calculated as TiO2. This reduced solution is added to the titanyl sulfate solution produced by sulfuric acid decomposition of the relatively iron-free slag, their relative proportions being such as to provide a titanium (III) content of 0.1 to 4 grams per liter calculated as TiO2. This prevents formation of trivalent iron which would pose a problem during later production of pigment. A portion of the resultant solution is then recycled for reduction of titanium IV to titanium (III) by additional iron and sulfuric acid.

Unite States Patent 1191 Kienast et al.

1451 Apr. 17, 1973 1 PRODUCTION OF TITANYL SULFATE SOLUTIONS [73]Assignee: Farbeniabriken Bayer Aktiengesellschaft, Leverkusen, Germany[22] Filed: Mar. 17, 1971 [21] Appl. No.: 125,153

[30] Foreign Application Priority Data [56] References Cited UNITEDSTATES PATENTS 1,831,852 11/1931 Farup ..23/l17 X 2,309,988 2/1943 Ryanet al. ..23/l17 2,794,702 6/1957 Allan et al. ..23/1 17 2,850,357 9/1958Myers et a1 ..23/1 17 3,218,131 11/1965 Grose et a1 ..23/202 R 3,341,291/1967 Mabbs et al. ..23/202 R 3,441.373 4/1969 Bonsack ..23/117 x3,486,847 12/1969 Steinhausen ..23/1 17 3,615,204 10/1971 Libera et 1.23/117 Primary Examiner-Edward Stern Attorney-Burgess, Dinklage 8LSprung ABSTRACT A titaniumand iron-containing slag is ground, the ironis magnetically separated and the balance is decomposed with sulfuricacid to produce a titanyl sulfate solution which is further treated torender it suitable for preparation of superior titanium dioxidepigments.

Specifically, a portion of the ultimate titanyl sulfate solution issubjected to reduction by the addition thereto of magnetically separatediron and sulfuric acid, the reduction being carried out to give atitanium(ll1)content of about 50 to 90 grams per liter calculated as TiOThis reduced solution is added to the titanyl sulfate solution producedby sulfuric acid decomposition of the relatively iron-free slag, theirrelative proportions being such as to provide a titanium (111) contentof 0.1 to 4 grams per liter calculated as T10 This prevents formation oftrivalent iron which would pose a problem during later production ofpigment. A portion of the resultant solution is then recycled forreduction of titanium 1V to titanium (111) by additional iron andsulfuric acid.

PATENIEM W 3.728.431

SHEET E-UF 2 Gerhard Kienast, Heribert StUtgens, Hans Gunter ZanderINVENTORS PRODUCTION OF TITANYL SULFATE SOLUTIONS According to US. Pat.No. 2,531,926, titanium slags which contain about 65 to 90 percent ofTiO,, 1 to 16 percent of metallic iron and iron compounds and 8 to 20percent of oxides such as silicic acid, calcium oxide, magnesium oxideand/or aluminum oxide are decom posed with concentrated sulfuric acid.In this process, the slag which has been finely ground in a ball mill isreacted with sulfuric acid without the metallic iron being firstremoved. This process has the disadvantage that the metallic iron stillcontained in the slag reacts with the sulfuric acid used fordecomposition to form hydrogen which may be produced in such largequantities that the lower limit of explosion is exceeded.

In the decomposition of titanium slags with sulfuric acid, solublesulfates are formed which are present in a solid form known asdecomposition cake. The reduced titanium compounds originally present inthe titanium slag, amounting to about 10 percent, are usually oxidisedcompletely under the conditions of decomposition into Ti(lV) compounds.By extracting this residue with water, a strong sulfuric acid solutionis obtained which contains mainly titanyl sulfate and ferrous sulfate.This solution is clarified and filtered and may than be concentrated ifdesired. As is well known, the titanium sulfate solution obtained in theso-called sulfate process for the production of titanium dioxidepigments by decomposition of titanium slag with sulfuric acid followedby dissolving the decomposition cake is reduced by the introduction ofmetallic iron,

e.g., iron scrap. The Fe ions are first converted into Fe ions becausethe salts of divalent iron do not hydrolyze so readily as the salts oftrivalent iron, i.e., they are not decomposed by hydrolysis under theconditions of the subsequent hydrolysis of the titanium salts by heat,and therefore cannot contaminate the titanium hydrolysate. In order toensure that no more Fe ions will occur, it is customary to continue thereduction to the stage where a small amount of Ti ions is still presentafter hydrolysis (U.S. Pat. No. 2,309,988 and German Auslegeschrift1,270,016).

' In US. Pat. No. 2,049,504, a process is described in which a solutionwhich contains tetravalent titanium and trivalent iron is treated with aTi(III) salt solution which has been prepared separately by thereduction of a Ti(lV) salt solution. Reduction of the tetravalenttitanium is carried out with at least two metals which have an electricpotential somewhere between calcium and hydrogen. In this process, themetals are used in a relatively coarse form. Iron alone, especially in afinely divided state, is not suitable.

According to US. Pat. No. 2,416,216, sponge iron is used as reducingagent. This can be obtained by treating titanium iron ores with reducinggases or materials which contain carbon.

The action of finely divided iron which has been obtained by reducingfinely ground titanium iron ore on a clarified solution containingtetravalent titanium and trivalent iron has also been proposed (U.S.Pat. No. 3,416,885).

Ilmenite decomposition processes which result in solutions having a veryhigh concentration or iron (III) sulfate cannot readily be applied tothe working up of titanium slag. It is accordingly anobject of theinvention to provide titanyl sulfate solutions which are free oftrivalent iron.

This and other objects and advantages are realized in accordance withthe present invention which provides a process for the treatment oftitanium containing slag to prepare sulfuric acid titanyl sulfatesolutions which are free from ferric iron by grinding and drying,decomposition with sulfuric acid, separation of solids which have notbeen decomposed and optionally evaporation of the solution obtained bythe decomposition reaction, the decomposition solution being adjusted toa Ti(III) concentration sufficient to prevent the formation of iron(III) ions. In this process the metallic iron contained in the slag ismagnetically separated from the gravel returned from a grinding anddrying process and is added to a partial stream of the titanyl sulfatesolution which has been freed of the decomposition residue, the ironbeing added in such an amount that the titanium (III) concentration inthis partial streamis adjusted to about 5.0 to g/l, based on the amountof TiO and this partial stream is then returned to the entiredecomposition solution.

The magnetically separated iron has a particle size of about 40 to ,350microns, preferably about 80 to microns. Its addition to theconcentrated Ti(III) salt solution is advantageously controlled by meansof the Redox potential measured in the decomposition solution.

Crude slags which contain titanium to an extent of more than about 60percent to Ti0 may be used as a starting material for the process of theinvention. Such slags also contain metallic iron, iron compounds andSiO, in addition to calcium oxide, magnesium oxide and aluminum oxide. 1

The slag must first be ground in order to bring the raw material into aform suitable for decomposition. The object of the grinding operation isto obtain a material with optimum particle sizes so that the subsequentdecomposition with sulfuric acid will proceed sufficiently rapidly.Grinding the material even more finely is of no advantage in view of thehigher energy consumption and loss in efficiency of the grinding mill.It is desired to obtain a particle size distribution having a frequencymaximum at about 20 microns.

The grinding may be carried out in tube mills. These mills, which arefilled with steel balls, operate on the principle of a rotary siftermill. The stream of air passed through the mill may be heated, e.g., byan oven, so that it serves at the same time to dry the ground materialto a residual moisture content of about 0.1 percent by weight of water.

The material discharged from the mill, e.g., by pneumatic means, neednot yet have its final degree of fineness because it will subsequentlybe separated in a sifter into fine material and grit which is returnedto the mill. The fine material which is to be decomposed is separatedfrom the accompanying air in a cyclone and collected in bins.Decomposition of the fine material is then carried out with sulfuricacid in known manner.

For this purpose, concentrated sulfuric acid is added to the finelyground material in large conical tanks. Steam is then directlyintroduced into this mixture with constant pneumatic stirring until thedecomposition reaction starts. Temperatures of between about 200 and 220C are reached in the course of this reaction. A

solution highly acidified with sulfuric acid is obtained by extractingthe resulting decomposition cake with water. This solution is thenclarified and if desired evaporated to a concentration of about 200 to280 g of TiO per liter. According to the invention, the concentratedTi(IlI) sulfate solution is added to the decomposition solution eitherbefore or after clarification and filtration. The resulting titanylsulfate solution may then be subjected to hydrolysis by heat to produce0,.

The crude slag used as starting material for the process of theinvention still contains 0.6 to 0.9 percent of metallic iron. Since thismust be removed before the decomposition with sulfate acid, it isseparated-magnetically from the non-magnetizable particles of thetitanium slag. The proportion by weight of the magnetic fraction basedon the quantity of raw material which is to be ground up is betweenabout 0.5 and 1.0 percent. According to theinvention, the magneticseparation is carried out in the return flow of grit. The iron separatedin this way has a particle size of about 40 to 350 microns, preferablyabout 80 to 180 microns. Once the flow is established, the metallic ironin the return flow of grit is concentrated to about 6 to 10 times theintial concentration. The magnetic separation may be carried out e.g.,by th process of German Patent Specification 735,356.

For magnetic separation, numerous permanent magnets which have segmentalpole ends are arranged over a width of l m in a horizontal drum made ofnon-magnetizable material. The drum rotates in the direction of the flowof product while the magnets inside the drum move in the oppositedirection at a moderate speed. The mixture containing metallic iron isfed to the drum from a vibrating chute which has a transversedistributing function. The non-magnetizable constituents are thrown offdue to the high speed of rotation and return to the mill as grit returnflow. The magnetizable iron adheres to the drum until it is removed by abrush roller diametrically opposite to the feed point. The continuousflow of magnetically separated iron intothe containers may be monitored,e.g., by electromagnetic means.

According to the invention, the iron obtained in this The reductionyield according to the following reaction equations:

Fe, s0, Fe -s3 Peso and 2 TiOSO, Fe 2 H,SO Ti,(SO FeSO 2 H O was foundto be about 60 to 85 percent, calculated from the weight of metalliciron put into the reaction The iron separated from the return flow ofgrit obtained from the process of grinding and drying is eminentlysuitable for the preparation of solutions which contain Ti(IIl). w

For the preparation of the Ti(lll) solutions, it is ad'- vantageous touse a partial stream of decomposition solution which has been clarified,i.e., freed from solid residue. Since the solutions are adjusted-to highconcentrations of Ti(lII) sulfate, the volume of the partial stream isvery small in proportion to the-total amount of decomposition solution.About 2 percent by volume to 4 percent by volume are generallysufficient.

The following conditions are especially suitable for the preparation ofthe Ti(lll) salt solution:

The Ti(IV) sulphate solution which is to be reduced should be moredilute than the decomposition soluway (the increase in concentrationafter the magnetic 7 separation is about to percent of metallic ironfrom-a concentration of about 0.6 to 0.9 percent in the slag) is usedfor preparing a Ti(lll) salt solution by reduction of a Ti(IV) saltsolution. These Ti(lll) sulphate solutions, which with their highcontent in Ti(lll) ions are resistant to oxidation and hydrolysis for asmuch as. several weeks, have a concentration of about 50 to g/l,preferably about 70 to 80 g/l of reduced titanium compounds, calculatedas Ti0,.

The titanium (llI) sulfate solution is used to reduce any iron (lII)sulfate present in the solution obtained from the decomposition oftitanium slag, this reduction being carried out either before or afterclarification and filtration and in accordance with the followingequations:

tions. At the end of the reaction, the total amount of trivalent andtetravalent titanium in the reduced solution, calculated as TiO shouldnot be higher than about g/l. It is suitable to use already dilutedtitanium sulphate solutions, for example those obtained by clarificationof the decomposition solution. It is advantageous to use the filtrate ofthe thickener underflow pulp obtained by clarification of the titaniumsulfate solutions in an overflow thickener. The wash water used forwashing out the separated solids is advantageously combined with thefiltrate. In these relatively dilute solutions, the total conversion totrivalent titanium compounds is greater than in more concentratedstarting solutions. Moreover, diluting the starting solution ensuresthat the FeSO, previously present and that newly formed by the additionof iron cannot so readily crystallize together with the Ti(lll) sulfateon subsequent cooling of the solution.

Sulfuric acid is added to the solution which is to be reduced, in orderto have a sufficient excess of acid for dissolving the iron. Theformation of iron sulfate must nottake place at the cost of thefreesulfuric acid originally present in the titanium sulfate solution.

Reduction should start aLabout 30 to 50 C. Temperatur es of 60 to 65 C.are reached only subsequently in the course of the reaction as a resultof the heat evolved. It is necessary to ensure by suitable control oftheaddition of iron and if necessary by cooling that a temperature ofabout 65 C. is not exceeded during the reduction because temperaturesabove 65 C. considerably promote the evolution of hydrogen.

The particle size distribution of the iron powder added should beadjusted about 40 to 350 microns and preferably about 80 to microns sothat the iron will not react spontaneously because in that case theevolution of hydrogen would predominate over the reduction of Ti(lV). Onthe other hand, the particles must be sufficiently fine to ensurecomplete chemical solution of the particles within about 10 to 15minutes after they have been added.

It has been found advantageous to suspend the finely divided iron inwater and to pump this suspension into the Ti(IV) sulfate solution whichis acidified with sulfuric acid. This method enables the addition ofiron to be more easily adjusted and controlled. The particles of ironwetted with water are introduced into the reaction solution about 1 mbelow the liquid surface by means of an immersion tube which is open tothe atmosphere at the top.

By this method, the evolution of hydrogen and hence the loss in yield ofreduction product are kept very low in the industrial production ofTi(III) sulfate solution.

The addition of concentrated Ti(III) salt solution is controlled by theRedox potential measured in the decomposition solution.

When measuring the Redox potential during the addition of Ti( III)sulfate to the decomposition solution, the transition from the oxidationpotential of Fe(III) ions to the reduction potential of Ti(III) ionsregisters a jump of several hundred millivolts. The value in millivoltsmeasured by means of a Redox electrode measuring chain, e.g., a platinumelectrode with Ag/AgCl electrode as reference electrode, may serve as ameasure of the concentration of Fe(III) ions and Ti(III) ions.

It is therefore possible to find the actual value of the content inFe(III) ions or Ti (III) ions from the measured potential value and tolay down a particular potential value as the nominal value to which theconcentration of Ti(III) ions is to be adjusted. These two values ofpotential may be used to control a regulating mechanism by which thequantity of Ti(III) sulfate solution required is supplied through aregulating valve.

The invention will be further described with reference to theaccompanying drawings wherein:

FIG. 1 is a flow sheet of the whole process; in the ,flow sheet thefigures have the following meaning: 101

is the titanium slag, 102 grinding and drying, 103 magnetic separation,133 separated metallic iron, 113 production of a concentratedTi(III)-solution, 123 storage tank for the Ti(III)-solution, 143sulfuric acid for the production of Ti(III)-solution, 153 a partialstream of Ti(IV)-solution, 114 sulfuric acid for the digestion process,124 water, 104 digestion step, 105 reduction of the Fe(III) andadjustementof the necessary Ti(III)-concentration, 106 clarification andfiltration, 107 concentration, 108 thermal hydrolysis and 109 is thefinal product TiO FIG. 2 is a schematic view of the apparatus forproducing a titanyl sulfate solution containing Ti(III) in about 50 to90 grams per liter; and

FIG. 3 is a schematic view of the apparatus for producing a titanylsulfate solution containing about 0.1 to 4 grams per liter of Ti(III)from decomposition solution and the product of FIG. 2.

In the drawings, the reference numeral 1 (in FIG. 2) denotes a storagebin for dilute Ti( IV) sulfate solution, 3 the reaction vessel, 4 acontainer for measuring sulfuric acid, 6 and 16 connection pipes throughwhich air or steam may be supplied for pneumatic stirring or heating, 7a cooler, 9 a storage bin for iron which is supplied to a stirrer vessel11 by means of a ball valve 10, the reference numerals 13, 17 and 18represent valves, 2, 5, 8 and 12 represent pumps, a ventilator and 19 avessel for clarifying the titanium (III) sulfate solution. In FIG. 3,reference numeral 20 represents the supply of concentrated Ti(lll)solution, 21 a storage bin, 22 the decomposition tank, 23 a feed pipeinto the stirrer vessel 24, 25 a circulating pump, 26 an electrodevessel, 27 a potentiometer, 28 a control apparatus and 2F a regulatingvalve for the feed pipe 30.

The embodiment of the process of the invention described hereinafter andshown diagrammatically in FIGS. 2 and 3 is particularly suitable.

A certain volume of dilute titanyl sulfate solution (rotary filterfiltrate) is delivered into the conical reaction vessel 3 from a storagetank 1 by means of a pump (FIG. 2). Concentrated sulfuric acid, thequantity of which has previously been measured in a separate vessel 4,is then added to the titanyl sulfate solution already in the reactionvessel 3 by means of the pump 5. The reactants are mixed by pneumaticstirring, air being blown in from below through the pipe 6. The heat ofdilution produced may be removed in a cooler 7 while the mixture iscirculated by means of the pump 8, thereaction mixture being at the sametime adjusted to the required starting temperature for the reductionreaction. If on subsequent addition of iron the reaction becomes toovigorous due to increase in temperature, the excess heat of reaction mayalso be removed during the reduction process by cooling the titaniumsulfate solution in the cooler to maintain the required temperature.

The quantity of iron powder required for the reduction is delivered fromthe storage bin 9 into a stirrer vessel 11 by means of a ball valve 10and suspended in the given quantity of water in this vessel. Now that itis suspended in water, the iron powder can be pumped and delivered tothe titanyl sulfate solution by means of a double channel gear wheelpump 12. By appropriately setting the valves 13, the quantity of ironsupplied can be accurately controlled. The suspension flows in throughthe immersion tube 14 which is open at the top. A ventilator 15 preventsaccumulation of any hydrogen formed in the reaction vessel so as toensure vigorous suction. The concentration of hydrogen is constantlycontrolled by measuring instruments. Steam may be supplied together withthe air for pneumatic stirring through the pipes 16 in order to increasethe temperature of the reaction mixture if necessary. After the solutionhas been reduced and clarified by sedimentation, it enters a storagetank for concentrated Ti(III) sulfate solution through a conduit andvalve 17. The lower part of the contents of the conical container isdischarged through the valve 18, and the clear solution is separatedfrom it by decanting in a separate vessel 1. While clarified Ti( Ill)sulfate solution flows over to the storage tank, solid residue whichcannot be used settles'in the lower part of this vessel and can becarried away in it.

The concentrated titanium (III) sulfate solution enters the storage tank21 from a reaction vessel (e.g., reaction vessel 3 of FIG. 2) throughthe overflow 20 (FIG. 3). The solution obtained after sulfuric aciddecomposition of the titanium slag from which iron was magneticallyseparated is discharged from the decomposition tank 22 into the stirrervessel 24 through the pipe 23. After the inflow of the decompositionsolutions which are obtained intermittently, this stirrer vessel alsoserves as storage vessel from which overflow thickeners can becontinuously supplied with production solution. At the same time, averysmall partial stream of the solution is continuously pumped from thestirrer vessel 24 through the electrode vessel 26 by means of the pump25. This electrode vessel contains a platinum electrode with an Ag/AgClelectrode as reference electrode.

The Redox potential of the solution is determined by connecting theelectrode to a potentiometer 27. When the Redox potential differs fromthe nominal value, the governor 28 opens the control valve 29 so thatthe appropriate quantity of titanium (III) sulfate solution can flowfrom the container 21 into the stirrer vessel 24 i through the pipe30.'This process continues until sufficient Ti(III) sulfate solution hasbeen added and the Ti(lII) ion concentration has reached the requiredvalue and the Redox potential has been adjusted to the nominal value.Decomposition solutions continuously and intermittently entering thestirrer vessel are thus adjusted to the required Ti(III) ionconcentration by this regulating mechanism. Even higher accuracy in theadjustment of the concentration of Ti(llI) ions can be achieved if about90 percent of the quantity of Ti(III) sulfate solution which is requiredaccording to the Redox potential is introduced into a first intermediatevessel and the remaining approximately percent are introduced into asecond intermediate container. By this method, the decompositionsolution can be ad- 'justed to an accuracy of 0.1 g/l of trivalenttitanium calculated as TiO,.

The effluent from vessel 24 is then sent to the overflow thickeners (notshown), a portion thereof being withdrawn and sent to vessel 1 forproducing adiditonal titanium (Ill).

This process is shown schematically in the flow sheet of FIG. 1, alongwith an alternative shown in broken lines. In the alternative, thesulfuric acid solution of titanyl sulfate obtained by decomposition ofthe relatively iron-freev slag can be diluted and a portion thereof sentto the vessel wherein the reactions'with the iron takes place in orderto produce Titanium(lll), this portion replacing the portion sent fromthe clarifier in whole or in part. Since in this broken-line alternateclarification is carried out before adjustment of the Ti (III) content,subsequent clarification can be omitted and the solution directly passedto hydrolysis as shown I centration which is accurate to 0.1 g/l resultin a low consumption of reducing agent so that combined with themagnetically separated iron, the use of iron raw material is reduced toone-third to one-fourth compared with previous methods. Furthermore, byeffect ing the reduction with iron scrap in a single decompositionvessel rather than in multiple vessels, the number of pieces ofequipment which are liable to need repair EXAMPLE 1 Preparation of aconcentrated Ti(lll) sulfate solution (Laboratory preparation) 25 g of afraction which has been magnetically separated from ground titaniumslags were added in thecourse 1 hour to a mixture of 300 cc of rotaryfilter filtrate from the decomposition plant, 40 cc of concentrated H80, and cc of H 0 with stirring. The proportion of metallic Fe was 74percent, the particle size between 40 and-120 microns. At the end of thereac* tion, the amount of solution was 380 cc; there was a slight lossin volume due to evaporation. On analysis, the solution was found to becomposed as follows:

Ti (total) in terms of H0, 121 g/l Ti (trivalent) in terms of TiO, 83gll H,SO (free and bound) 440 g/l FeSO. 179 3]] Conversion to Ti 69%Yield based on Fe metal EXAMPLE 2 The following quantities were putthrough the mill used forcontinuous grinding and drying of titaniumslag:

Crude slag introduced into the apparatus 330 000 kg Ground materialobtained in particles of 40 microns 328 000 kg Magnetically separatedfraction -180 microns 2 000 kg The ground material contained less than0.2'percent Fe. Analysis of the magnetic fraction was as follows:

Fe metal 66.5% FeO 15.2% TiO, 14.4% Remainder 3.9%

The magnetically separated 2,000 kg with 1,330 kg of Fe metal weresuspended in 7.7 m of water which was also necessary for the subsequentreaction as water of dilution. This iron suspension was pumped in thecourse of one hour through the immersion tube into the solution whichwas prepared as follows:

24.5 m of filtrate of the rotary filter were mixed with 4 m ofconcentrated sulfuric acid in the reaction vessel, 28 m of a solution ofthe following composition being obtained:

Ti (total) in terms of TiO, g/l Ti (trivalent) as TiO, 1 g/l 11,80.(free and bound) 565 gll FeSO The reaction took place with vigorouspneumatic stirring and the temperature rose from 47 to 62 C.

After a brief restirring and sedimentation of the unreacted particles 36m of a clear solution were obtained which was composed as follows:

Ti (total) in terms of TiO, 125 g/l Ti (trivalent) in terms of TiO, 87g/l H 80 (free and bound) 425 g/l reso 146 g/l During the wholereaction, the concentration of hydrogen in the discharged air from thestirrer did not rise above 2%. The conversion was 70 percent and thereduction yield 82 percent. The fact that the iron .the concentration ofTi(III) ions in thedecomposition solution to the nominal value. Theappropriate analyses show the following results:

Before addition After Addition to the decomposition solution Ti (totalin terms of Ti 235 g/l 232 gll Ti (trivalent) in terms of TiO, 1.4 g/lFe (total) in terms of FeSO, 92 g/l 94 g/l Fe in terms of Fe,(SO.), 2 H80 (free and bound) 524 gll 521 g/l The consumption of concentratedTi(III) sulfate solution was 1.12 times the theoretical amount.

EXAMPLE 3 A Ti(lII) sulfate solution prepared commercially and havingthe following composition:

Ti (total) in terms of TiO, 130 g/l Ti (trivalent) in terms of TiO, 75

H 80 (free and bound) 450 g/l Feso, o gll was used to reduce thetrivalent iron in decomposition solutions of titanium slag and to adjustthe concentration of Ti ions to the value required for carrying out atrouble-free hydrolysis.

cc of the above Ti(lll) sulfate solution were added to 500 cc of asolution obtained from the process of decomposition of titanium slag(Time: 2 minutes):

Analysis before Analysis after addition addition Ti (total) in terms ofTiO, 236 3/] 235 g/l Ti (trivalent) in terms of TiO, 1.6 g/l Fe (total)in terms of FeSO, 89 g/l 92 g/l Fe in terms of Fe,(SO 3 g/l H,SO freeand bound 520 g/] 517 g/l It will be appreciated that the instantspecification and examples are set forth by way of illustration and notlimitation, and that various modifications and changes may be madewithout departing from the spirit and scope of the present invention.

What is claimed is: I

In the preparation of a sulfuric acid-containing solution of titanylsulfate wherein a titaniumand ironcontaining slag is ground, decomposedwith sulfuric acid and separated from undissolved decomposition residue,the improvement which comprises magnetically separating from the groundslag iron of a particle size of about 40 to 350 microns, withdrawingfrom the main body of the sulfuric acid-containing solution of titanylsulfate a portion thereof, adding to the withdrawn portion themagnetically separated iron while maintaining a maximum temperature ofabout 65 C, whereby the reaction between iron and sulfuric acid servesto reduce titanium IV in the withdrawn portion to titanium (III), therelative proportions of iron and titanyl sulfate solution being suchthat the titanium (III) concentration in the resulting reduced solutionis from about 50 to grams per liter calculated as TiO and adding saidreduced solution to the main body of the sulfuric acid-containingtitanyl sulfate solution in amount to provide a titanium (XII) contentof 0.1 to 4 grams per liter calculated as TiO whereby if any iron II ispresent in said main body of the solution it is prevented from going totrivalent state.

2. Process according to claim 1, wherein the magnetically separated ironis suspended in water, and the aqueous suspension of iron is added tothe withdrawn portion of the sulfuric acid-containing solution oftitanyl sulfate.

3. Process according to claim 2, wherein the aqueous iron suspension isintroduced into the titanyl sulfate solution below the surface of thesolution.

4. Process according in claim 3, wherein the magnetically separated ironhas a particle size between about 80 and microns.

5. Process according to claim 1, wherein the addition of the reducedsolution is controlled by the Redox potential measured in the main bodyof the titanyl sulfate solution.

6. Process according to claim 4, wherein the addition of the reducedsolution is controlled by the Redox potential measured in the main bodyof the titanyl sulfate solution, the Redox potential being set toprovide a titanium (III) content of 1.3 to 1.6 grams per litercalculated as TiO

2. Process according to claim 1, wherein the magnetically separated ironis suspended in water, and the aqueous suspension of iron is added tothe withdrawn portion of the sulfuric acid-containing solution oftitanyl sulfate.
 3. Process according to claim 2, wherein the aqueousiron suspension is introduced into the titanyl sulfate solution belowthe surface of the solution.
 4. Process according in claim 3, whereinthe magnetically separated iron has a particle size between about 80 and180 microns.
 5. Process according to claim 1, wherein the addition ofthe reduced solution is controlled by the Redox potential measured inthe main body of the titanyl sulfate solution.
 6. Process according toclaim 4, wherein the addition of the reduced solution is controlled bythe Redox potential measured in the main body of the titanyl sulfatesolution, the Redox potential being set to provide a titanium (III)content of 1.3 to 1.6 grams per liter calculated as TiO2.